3. Where is the Water ?Where is the Water ?
Figure 16.2
4. Groundwater is a ResourceGroundwater is a Resource
The amount of groundwater is vast butThe amount of groundwater is vast but
not unlimited.not unlimited.
About 0.6% of the world's water foundAbout 0.6% of the world's water found
underground.underground.
It provides:It provides:
50% of the world's drinking water50% of the world's drinking water
40% of the water used for irrigation40% of the water used for irrigation
25% of industry's needs25% of industry's needs
5. Nevertheless, in many placesNevertheless, in many places
overuse and misuse has resultedoveruse and misuse has resulted
in:in:
• streamflow depletionstreamflow depletion
• land subsidenceland subsidence
• saltwater intrusionsaltwater intrusion
• increased pumping costs fromincreased pumping costs from
ever deeper suppliesever deeper supplies
• contaminationcontamination
6. What is Groundwater?What is Groundwater?
Groundwater is waterGroundwater is water
that is foundthat is found
underground in theunderground in the
cracks and spaces incracks and spaces in
soil, sand, and rocks.soil, sand, and rocks.
Groundwater is stored inGroundwater is stored in
—and moves slowly—and moves slowly
through—geologicthrough—geologic
formations calledformations called
aquifersaquifers..
7. Distribution of GroundwaterDistribution of Groundwater
Groundwater is
typically
misunderstood:
Underground
“lakes” and
“rivers” are rare
Most underground
water exists in
spaces between
grains (in “pore
spaces”)
8. Distribution of GroundwaterDistribution of Groundwater
• Zone of AerationZone of Aeration – The area– The area
above the water table thatabove the water table that
includes the zones soilincludes the zones soil
moisture and capillary fringe.moisture and capillary fringe.
• Soil MoistureSoil Moisture – Groundwater held– Groundwater held
by molecular attraction as aby molecular attraction as a
surface film on soil particles.surface film on soil particles.
Used by plants for life functionsUsed by plants for life functions
including transpiration.including transpiration.
• Capillary FringeCapillary Fringe – Immediately– Immediately
above the water table, whereabove the water table, where
groundwater is held by surfacegroundwater is held by surface
tension in the spaces betweentension in the spaces between
the grains of soil or sediment.the grains of soil or sediment.
• Zone of SaturationZone of Saturation – Zone– Zone
where all of the open spaceswhere all of the open spaces
between the soil/sedimentbetween the soil/sediment
grains is completely filledgrains is completely filled
with water.with water.
• Water TableWater Table – The upper limit of– The upper limit of
the zone of saturation.the zone of saturation.
• GroundwaterGroundwater – Water held within– Water held within
the zone of saturation.the zone of saturation.
9. How Does Groundwater Move?How Does Groundwater Move?
Underground, waterUnderground, water
slowly moves from anslowly moves from an
aquifer’saquifer’s rechargerecharge
areasareas (areas where(areas where
water seeps into thewater seeps into the
aquifer from rain fall,aquifer from rain fall,
snow melt, etc.) to it’ssnow melt, etc.) to it’s
discharge areadischarge area (like(like
streams, springs andstreams, springs and
lakes).lakes).
Groundwater is alwaysGroundwater is always
moving (this is calledmoving (this is called
groundwater flowgroundwater flow ) and) and
moves very slowly--moves very slowly--
only inches per year.only inches per year.
groundwater flow discharge area
evaporation
recharge area
precipitation
condensation
runoff
transpiration
aquifer
water table
infiltration
Hydrologic Cycle
10. Water Table FormationWater Table Formation
Water Table Formation Animation #95Water Table Formation Animation #95
11. The water table is rarely level; it isThe water table is rarely level; it is
a subdued replica of the surfacea subdued replica of the surface
topography. This reflects:topography. This reflects:
Variations in rainfall (seasonal).Variations in rainfall (seasonal).
The slow rate at which water movesThe slow rate at which water moves
through the subsurface.through the subsurface.
The effects of gravity.The effects of gravity.
Where a stream, lake or swamp isWhere a stream, lake or swamp is
found, the water table coincidesfound, the water table coincides
with the surface of the body ofwith the surface of the body of
water.water.
12. Gaining Streams – Gain
water from the inflow of
groundwater through the
streambed
(the elevation of the
water table must be
higher that the elevation
of the surface of the
stream).
Losing Streams –
Streams that lose water
to the groundwater
system by outflow
through the streambed
(the elevation of the
water table is lower than
the elevation of the
surface of the stream).
Figure 17.4
13. Factors Influencing theFactors Influencing the
Storage and Movement ofStorage and Movement of
GroundwaterGroundwater
Rock and sediment contain voidsRock and sediment contain voids
called pore spaces.called pore spaces.
TheThe porosityporosity is the percentage ofis the percentage of
the total volume of rock thatthe total volume of rock that
consists of pore spaces. Theconsists of pore spaces. The
quantity of water that can bequantity of water that can be
stored depends on the porosity.stored depends on the porosity.
14. How is Porosity Measured?How is Porosity Measured?
Porosity(%)=Porosity(%)= Vol. of Pore SpaceVol. of Pore Space x 100%x 100%
Total VolumeTotal Volume
See the following exampleSee the following example
15. Assume youAssume you
have twohave two
graduatedgraduated
cylinders,cylinders,
one with 5one with 5
ml. of sand,ml. of sand,
the otherthe other
with 5 ml. ofwith 5 ml. of
water.water.
17. Suppose thatSuppose that
after lettingafter letting
the waterthe water
settle, theresettle, there
remains 4 mlremains 4 ml
of waterof water
above theabove the
sand; what issand; what is
the porosity?the porosity?
18. The SolutionThe Solution
You started with 5 ml. of Sand; thisYou started with 5 ml. of Sand; this
includes both the sand and the poreincludes both the sand and the pore
space, in other words this is thespace, in other words this is the TOTALTOTAL
VOLUMEVOLUME
You poured in 5 ml of water, 4 mlYou poured in 5 ml of water, 4 ml
remained above the sand, 1 ml went intoremained above the sand, 1 ml went into
the sand. Where did it go? Into the pores.the sand. Where did it go? Into the pores.
TheThe PORE SPACE VOLUMEPORE SPACE VOLUME = 1 ml.= 1 ml.
1ml/5ml x 100% = 20% Porosity1ml/5ml x 100% = 20% Porosity
19. Different Rock Types HaveDifferent Rock Types Have
Different PorositiesDifferent Porosities
Sediment might have porosities from 10 toSediment might have porosities from 10 to
50%.50%.
The porosity of most igneous andThe porosity of most igneous and
metamorphic rocks is less than 1%.metamorphic rocks is less than 1%.
Porosity in sediments tends to be:Porosity in sediments tends to be:
Higher if sediment is well sortedHigher if sediment is well sorted
Lower if sediment is well packedLower if sediment is well packed
Lower if sediment is well cementedLower if sediment is well cemented
Fractures can increase the porosity in igneous,Fractures can increase the porosity in igneous,
metamorphic rocks, and certain sedimentarymetamorphic rocks, and certain sedimentary
rocks (especially limestones).rocks (especially limestones).
20. The quantity of groundwater that can beThe quantity of groundwater that can be
stored depends on the porosity of thestored depends on the porosity of the
material.material.
21. TheThe PermeabilityPermeability of Rock isof Rock is
It’s Ability toIt’s Ability to TransmitTransmit WaterWater
Depends on porosity andDepends on porosity and
interconnectedness.interconnectedness.
Molecular attraction or surfaceMolecular attraction or surface
tension inhibits flow particularly intension inhibits flow particularly in
small pore spaces (shales).small pore spaces (shales).
AquifersAquifers are rocks with highare rocks with high
permeability (easily transmitpermeability (easily transmit
water).water).
AquitardsAquitards are impermeable (barrierare impermeable (barrier
to water flow).to water flow).
22. If pore spaces are too small,If pore spaces are too small,
surface tension keeps water fromsurface tension keeps water from
movingmoving
Aquitards Hinder orAquitards Hinder or
Prevent GroundwaterPrevent Groundwater
MovementMovement
24. Movement ofMovement of
GroundwaterGroundwater
Water must migrate through the pore spaces of rock.Water must migrate through the pore spaces of rock.
Only occasionally are there "underground rivers ofOnly occasionally are there "underground rivers of
water".water".
Underground water moves under aUnderground water moves under a hydraulic gradienthydraulic gradient ––
a slope to the water table.a slope to the water table.
Hydraulic headHydraulic head – the difference in height of the water– the difference in height of the water
table between the recharge and discharge points.table between the recharge and discharge points.
The flow rate orThe flow rate or velocityvelocity is governed byis governed by
Darcy's law: V = K h/lDarcy's law: V = K h/l
where V is the velocity, K is the is the permeabilitywhere V is the velocity, K is the is the permeability
coefficient, h is the hydraulic head, and l is thecoefficient, h is the hydraulic head, and l is the
horizontal distance between the recharge and dischargehorizontal distance between the recharge and discharge
points.points.
Velocities are typically several centimeters per day –Velocities are typically several centimeters per day –
very slow!very slow!
26. SpringsSprings
Outflow of groundwater that occurs where theOutflow of groundwater that occurs where the
water table intersects the earth's surface.water table intersects the earth's surface.
Or where there is aOr where there is a perched aquiferperched aquifer
29. Hot Springs and GeysersHot Springs and Geysers
Water in hot springs is 6-9°C (10-15°F)Water in hot springs is 6-9°C (10-15°F)
warmer than the mean annual airwarmer than the mean annual air
temperature.temperature.
Water in hot springs and geysers movesWater in hot springs and geysers moves
up from greater depths where it has beenup from greater depths where it has been
heated by the natural geothermal gradient,heated by the natural geothermal gradient,
or by cooling igneous bodies.or by cooling igneous bodies.
Primarily found in young geologicalPrimarily found in young geological
environments such as western U.S.environments such as western U.S.
30. Distribution of Hot SpringsDistribution of Hot Springs
and Geysersand Geysers in U.S.in U.S.
33. Deposits associated with geysers and hotDeposits associated with geysers and hot
springs at Yellowstone NP aresprings at Yellowstone NP are travertinestravertines oror
silica-richsilica-rich geyseritesgeyserites
34. WellsWells
Where water is artificially withdrawn from theWhere water is artificially withdrawn from the
earth.earth.
Result inResult in drawdowndrawdown of the water table – a conicalof the water table – a conical
depression in the water table known as adepression in the water table known as a cone ofcone of
depressiondepression..
Cone of depression increases the hydraulicCone of depression increases the hydraulic
gradient in the vicinity of the well. This may begradient in the vicinity of the well. This may be
good over the short-run, but has long-termgood over the short-run, but has long-term
adverse consequences.adverse consequences.
Lowers the water table overallLowers the water table overall
Cone of depression becomes largerCone of depression becomes larger
Reduces the column of water in contact withReduces the column of water in contact with
the wellthe well
35.
36. The Cone of DepressionThe Cone of Depression
Cones of Depression Animation #12Cones of Depression Animation #12
37. Artesian WellArtesian Well
Where the hydraulic gradient causesWhere the hydraulic gradient causes
the water in a well to move to a levelthe water in a well to move to a level
above the aquifer.above the aquifer.
Non-flowing artesian wellNon-flowing artesian well – water– water
does not come to the surface.does not come to the surface.
Flowing artesian wellFlowing artesian well – water rises to– water rises to
the surface and flows freely.the surface and flows freely.
38. Artesian WellArtesian Well
Must have the following conditions:Must have the following conditions:
Water must be confined to an inclined aquifer.Water must be confined to an inclined aquifer.
Aquitards must be present both above andAquitards must be present both above and
below the aquifer to keep the water frombelow the aquifer to keep the water from
escaping.escaping.
Friction reduces the artesian effect theFriction reduces the artesian effect the
further the well is from the recharge area.further the well is from the recharge area.
A city water supply system is a goodA city water supply system is a good
example of an artificial artesian system.example of an artificial artesian system.
42. Problems associatedProblems associated withwith
Groundwater WithdrawalGroundwater Withdrawal
Continued pumping (withdrawal)Continued pumping (withdrawal)
can lead to a drop in the watercan lead to a drop in the water
table.table.
Groundwater becomes aGroundwater becomes a
nonrenewable resourcenonrenewable resource
SubsidenceSubsidence
Saltwater IntrusionSaltwater Intrusion
